1. Field of the Invention
The present invention relates to a developing device used in an image forming device. In particular, the present invention relates to a developing device which prevents toner accommodated in a casing from leaking out of the casing from sliding surfaces between end portions of a developing roller and seal members.
2. Description of the Related Art
An image forming device including a developing device is used in a copy machine, a printer, a facsimile machine, and a digital Multi Function Peripheral (MFP) having a plurality of functions such as a copy function, a print function, a FAX communication function and a scanner function. In such an image forming device, a uniformly charged electrophotographic photoconductor is exposed selectively according to image information. An electrostatic latent image formed on the electrophotographic photoconductor is developed by the developing device, and a toner image is provided. When the toner image is transferred onto recording sheet (recording paper), an image recording process is carried out. Then, the unfixed toner image transferred on the recording sheet is fixed onto the recording sheet as a permanent image by a fixing device. In the developing device used in the image forming device, powdered toner is accommodated in a casing. In the casing, the toner is agitated at all times or periodically by an agitator and supplied to a developing roller. When the developing roller rotatably makes contact with a surface of the electrophotographic photoconductor, the electrostatic latent image is developed by the toner.
FIG. 5 illustrates a conventional developing device. An elastic blade 102 makes contact with an image forming region 305 on a surface of a developing roller 101. The elastic blade 102 frictionally charges toner 302 on the developing roller 101 and regulates the thickness of a layer of the toner 302. Therefore, a toner amount retained on the developing roller 101 is regulated. A seal member 104 makes contact with a non-image forming region 306 at each end portion of the developing roller 101. The seal member 104 is adhered on a position of a casing wall surface 103 corresponding to each end portion in an axial direction of the developing roller 101. Both end portions in the axial direction of the developing roller 101 are sealed by the seal members 104 to prevent leakage of the toner 302 from the end portions.
Although not illustrated in the drawings, in another known conventional developing device, a compressive deformation amount of a seal member is greater at an inner portion in an axial direction of a developing roller than end surfaces of the developing roller. In such a developing device, a portion of a casing wall surface where the seal member is mounted is arranged as a slanting surface. The inner portion in the axial direction of the developing roller is located higher than the end surfaces of the developing roller. In addition, the seal member is mounted on the casing wall surface and contacted against the developing roller. Accordingly, it is difficult for the toner 302 to leak from both end portions in the axial direction of the developing roller.
Referring to FIG. 5 again, accompanying the rotation of the developing roller 101, the toner 302, which has failed to pass through a nip portion, moves laterally along a tip end of the elastic blade 102 to the end portions of the developing roller 101 at an upstream side of the elastic blade 102 in a rotational direction of the developing roller 101. In many conventional developing devices, both end portions of the developing roller 101 are sealed by the seal members 104. However, when the toner 302 continuously moves laterally to the end portions of the developing roller 101, an escape route for the toner 302 disappears. Therefore, the toner 302 enters into a sliding surface 105 between the developing roller 101 and the seal member 104. As a result, the toner 302 may leak to the outside of the casing.
In particular, polymerized toner, which has been recently used frequently, has an extremely small particle diameter and has a shape that is close to a complete sphere. Therefore, the toner moves like a liquid and is prone to flow along a circumferential surface of the developing roller 101. Thus, there exists a problem that the toner may leak. The toner that leaks from the developing device causes a deterioration of an image quality or pollutes the surrounding area. In addition, the toner 302 is wasted.